Webservices

The basics

IDE: eclipse

UI designer: droiddraw

Android libraries: http://developer.android.com/resources/tutorials/hello-world.html
JSON and JSON web services for practice
(JavaScript Object Notation) is a lightweight data-interchange format.

http://www.json.org/

Picked JSON because I was originally doing the same thing with J2ME and it was a natural transition. Some JSON web service examples:

http://www.geonames.org/export/JSON-webservices.html

http://ws.geonames.org/earthquakesJSON?north=44.1&south=-9.9&east=-22.4&west=55.2 Thursday, 4 November 2010 2

Raw JSON:
{"earthquakes":[{"eqid":"2007hear","magnitude":8.4,"lng":101.3815,"src":"us","datetime":"2007-09-12 09:10:26","depth":30,"lat":-4.5172},{"eqid":"2007aqbk","magnitude":8,"lng":156.9567,"src":"us","datetime":"2007-04-01 18:39:56","depth":10,"lat":-8.4528},{"eqid":"2007hec6","magnitude":7.8,"lng":100.9638,"src":"us","datetime":"2007-09-12 21:49:01","depth":10,"lat":-2.5265},{"eqid":"a00043nx","magnitude":7.7,"lng":100.1139,"src":"us","datetime":"2010-10-25 12:42:22","depth":20.6,"lat":-3.4841},{"eqid":"2010utc5","magnitude":7.7,"lng":97.1315,"src":"us","datetime":"2010-04-06 20:15:02","depth":31,"lat":2.3602},{"eqid":"2009mebz","magnitude":7.6,"lng":99.9606,"src":"us","datetime":"2009-09-30 08:16:09","depth":80,"lat":-0.7889},{"eqid":"2009kdb2","magnitude":7.6,"lng":92.9226,"src":"us","datetime":"2009-08-10 17:55:39","depth":33.1,"lat":14.0129},{"eqid":"2010zbca","magnitude":7.6,"lng":123.533,"src":"us","datetime":"2010-07-23 20:51:11","depth":576.3,"lat":6.4939},{"eqid":"2010xkbv","magnitude":7.5,"lng":91.9379,"src":"us","datetime":"2010-06-12 17:26:50","depth":35,"lat":7.7477},{"eqid":"2007fubd","magnitude":7.5,"lng":107.6553,"src":"us","datetime":"2007-08-08 15:04:58","depth":289.2,"lat":-5.9682}]}

Indented:
{"earthquakes":

[

{

"eqid":"2007hear"

,"magnitude":8.4

,"lng":101.3815

,"src":"us"

,"datetime":"2007-09-12 09:10:26"

,"depth":30

,"lat":-4.5172

}

,{



}

]

}

Translated into Java:
package com.infostructure.experimental;

public class Earthquake {

public String eqid;

public String src;

public String datetime;

public double magnitude;

public double lng;

public double lat;

public double depth;

@Override

public String toString()

{

return "eqid: "+alertid+ " src: "+alerttext+ " datetime: "+alertdate;
}}
Getting your app to talk HTTP and JSON
WebService class

package com.infostructure.experimental;

import java.io.IOException;

import java.io.InputStream;

import java.io.UnsupportedEncodingException;

import java.net.HttpURLConnection;

import java.net.URL;

import java.net.URLConnection;

import java.net.URLEncoder;

import java.util.Map;

import org.apache.http.HttpResponse;

import org.apache.http.client.methods.HttpGet;

import org.apache.http.client.methods.HttpPost;

import org.apache.http.client.methods.HttpPut;

import org.apache.http.client.methods.HttpDelete;

import org.apache.http.client.params.ClientPNames;

import org.apache.http.client.params.CookiePolicy;

import org.apache.http.entity.StringEntity;

import org.apache.http.impl.client.DefaultHttpClient;

import org.apache.http.params.BasicHttpParams;

import org.apache.http.params.HttpConnectionParams;

import org.apache.http.params.HttpParams;

import org.apache.http.protocol.BasicHttpContext;

import org.apache.http.protocol.HttpContext;

import org.apache.http.util.EntityUtils;

import org.json.JSONException;

import org.json.JSONObject;

import android.util.Log;

import com.google.gson.Gson;

public class WebService{

DefaultHttpClient httpClient;

HttpContext localContext;

private String ret;

HttpResponse response = null;

HttpPost httpPost = null;

HttpGet httpGet = null;

HttpPut httpPut = null;

HttpDelete httpDelete = null;

String webServiceUrl;

//The serviceName should be the name of the Service you are going to be using.
public WebService(String serviceName){

HttpParams myParams = new BasicHttpParams();

HttpConnectionParams.setConnectionTimeout(myParams, 10000);

HttpConnectionParams.setSoTimeout(myParams, 10000);

httpClient = new DefaultHttpClient(myParams);

localContext = new BasicHttpContext();

webServiceUrl = serviceName;

}

//Use this method to do a HttpPost\WebInvoke on a Web Service

public String webInvoke(String methodName, Map<String, Object> params) {

JSONObject jsonObject = new JSONObject();

for (Map.Entry<String, Object> param : params.entrySet()){

try {

jsonObject.put(param.getKey(), param.getValue());

}

catch (JSONException e) {

Log.e("Groshie", "JSONException : "+e);

}

}

return webInvoke(methodName, jsonObject.toString(), "application/json");

}

// POST

private String webInvoke(String methodName, String data, String contentType) {

ret = null;

httpClient.getParams().setParameter(ClientPNames.COOKIE_POLICY, CookiePolicy.RFC_2109);

httpPost = new HttpPost(webServiceUrl + methodName);

response = null;

StringEntity tmp = null;

//httpPost.setHeader("User-Agent", "SET YOUR USER AGENT STRING HERE");

httpPost.setHeader("Accept", "text/html,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5");

if (contentType != null) {

httpPost.setHeader("Content-Type", contentType);

} else {

httpPost.setHeader("Content-Type", "application/x-www-form-urlencoded");

}

try {

tmp = new StringEntity(data,"UTF-8");

} catch (UnsupportedEncodingException e) {

Log.e("Groshie", "HttpUtils : UnsupportedEncodingException : "+e);

}

httpPost.setEntity(tmp);

Log.d("Groshie", webServiceUrl + "?" + data);

try {

response = httpClient.execute(httpPost,localContext);

if (response != null) {

ret = EntityUtils.toString(response.getEntity());

}

} catch (Exception e) {
Log.e("Groshie", "HttpUtils: " + e);

}

return ret;

}

// GET

//Use this method to do a HttpGet/WebGet on the web service

public String webGet(String methodName, Map<String, String> params) {

String getUrl = webServiceUrl + methodName;

int i = 0;

for (Map.Entry<String, String> param : params.entrySet())

{

if(i == 0){

getUrl += "?";

}

else{

getUrl += "&";

}

try {

getUrl += param.getKey() + "=" + URLEncoder.encode(param.getValue(),"UTF-8");

} catch (UnsupportedEncodingException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

i++;

}

httpGet = new HttpGet(getUrl);

Log.e("WebGetURL: ",getUrl);

try {

response = httpClient.execute(httpGet);

} catch (Exception e) {

Log.e("Groshie:", e.getMessage());

}

// we assume that the response body contains the error message

try {

ret = EntityUtils.toString(response.getEntity());

} catch (IOException e) {

Log.e("Groshie:", e.getMessage());

}

return ret;

}

public static JSONObject Object(Object o){

try {

return new JSONObject(new Gson().toJson(o));

} catch (JSONException e) {

e.printStackTrace();

}

return null;

}

public InputStream getHttpStream(String urlString) throws IOException {

InputStream in = null;

int response = -1;

URL url = new URL(urlString);

URLConnection conn = url.openConnection();

if (!(conn instanceof HttpURLConnection))

throw new IOException("Not an HTTP connection");

try{

HttpURLConnection httpConn = (HttpURLConnection) conn;

httpConn.setAllowUserInteraction(false);

httpConn.setInstanceFollowRedirects(true);

httpConn.setRequestMethod("GET");

httpConn.connect();

response = httpConn.getResponseCode();

if (response == HttpURLConnection.HTTP_OK) {

in = httpConn.getInputStream();

}

} catch (Exception e) {

throw new IOException("Error connecting");

} // end try-catch

return in;

}

public void clearCookies() {

httpClient.getCookieStore().clear();

}

public void abort() {

try {

if (httpClient != null) {

System.out.println("Abort.");

httpPost.abort();

}

} catch (Exception e) {

System.out.println("Your App Name Here" + e);

}

}

}

GSON
In order to get this class to compile, need to get the GSON library:

http://code.google.com/p/google-gson/

"
A Java library to convert JSON to Java objects and vice-versa"

…and add to your project’s build path.

User interface
Use droiddraw to put a basic UI together:

<?xml version="1.0" encoding="utf-8"?>

<AbsoluteLayout

android:id="@+id/widget0"

android:layout_width="fill_parent"

android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android">

<Button

android:id="@+id/btninvokeWebService"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="Invoke Web Service"

android:layout_x="10px"

android:layout_y="10px">

</Button>

</AbsoluteLayout>

Looks like this:


Put the generated XML code into "<YOUR_PROJECT_NAME>\res\layout\main.xml".
Security
To get Android to allow internet access, edit the Android project’s "AndroidMainfest.xml" file:

<manifest xlmns:android...>

...

<uses-permission android:name="android.permission.INTERNET">
</uses-permission> </manifest>
Putting it all together

A simple front-end that uses the "WebService" and "Earthquake" classes, the droiddraw UI output and by implication, the GSON library:

package com.infostructure.experimental;

import java.lang.reflect.Type;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

import com.google.gson.Gson;

import com.google.gson.reflect.TypeToken;

import android.app.Activity;

import android.os.Bundle;

import android.widget.EditText;

import android.widget.TextView;

import android.widget.Button;

import android.util.Log;

import android.view.View;

public class MainActivity extends Activity

{

private Button btninvokeWebService;

/** Called when the activity is first created. */

@Override

public void onCreate(Bundle savedInstanceState)

{

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

initControls();

}

private void initControls()

{

btninvokeWebService.setOnClickListener(new Button.OnClickListener() { public void onClick (View v){ invokeWebService(); }});

}

private void invokeWebService()

{

// Instantiate the Web Service Class with he URL of the web service not that you must pass

WebService webService = new WebService("http://ws.geonames.org/earthquakesJSON");

//Pass the parameters if needed

Map<String, String> params = new HashMap<String, String>();

params.put("north", "44.1");

params.put("south", "-9.9");

params.put("east", "-22.4");

params.put("west", "55.2");

//Get JSON response from server the "" are where the method name would normally go if needed example



String response = webService.webGet("", params);

try

{

//Parse Response into our object

Type collectionType = new TypeToken<List<Earthquake>>(){}.getType();

List<Earthquake> quakes = new Gson().fromJson(response, collectionType);

}

catch(Exception e)

{

Log.d("Error: ", e.getMessage());

}

}

}

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